The present invention relates to a belt-type fixing device that is used in an electrophotographic image forming apparatus.
In Japanese Patent Laid-Open Publication 2000-330412 has been disclosed a belt-type fixing device 50 shown in FIG. 4, for example. The belt-type fixing device 50 has an endless-sheet-like fixing belt 58, a rotatable heating roller 54 which has a heater 52 therein, and a rotatable fixing roller 56 which is away from the heating roller 54 and which has an elastic layer composed of rubber, for example, on an outer circumference thereof. The fixing belt 58 is wound around the heating roller 54 and the fixing roller 56. Furthermore, the belt-type fixing device 50 has a pressurizing roller 60 which can be driven to be rotated, which is in pressure contact with the fixing roller 56 through the fixing belt 58, and in which part in contact with the fixing belt 58 forms a fixing nip 62.
When the pressurizing roller 60 is driven to rotate in a direction of an arrow C in the belt-type fixing device 50, the fixing belt 58 rotates in a direction of an arrow D. While rotating in such a manner, the fixing belt 58 is subjected to heat transfer from the heating roller 54 heated by the heater 52, so that a temperature of the fixing belt 58 rises to a specified fixation temperature (e.g., to 180° C.). After the fixing belt is heated so as to have the specified fixation temperature, a paper having an unfixed toner image formed on an upper surface thereof is introduced into the fixing nip 62 in a direction of an arrow E, and the toner image is heated and fixed on the paper while the paper is passed through the fixing nip 62.
While the belt-type fixing device 50 is standing by for printing, a temperature of the heating roller 54 is kept at the specified fixation temperature by the heater 52 whereas temperatures decrease in the fixing roller 56, the pressurizing roller 60, and part of the fixing belt 58 that forms the fixing nip 62, which are away from the heating roller 54, because the fixing belt 58 is at rest. A problem therefore occurs in that it takes much time for the fixing nip 62 to retrieve the specified fixation temperature when the fixing belt 58 starts rotating upon reception of print starting signal.